The load in any given zone of an air conditioned building can vary substantially from time to time depending upon such factors as the occupancy of that zone at a given time, the load imposed by lights, computers, and other equipment that may be used within the zone, and the solar load that may be imposed upon the zone by solar energy transmitted thereinto through walls, roof, window openings, etc. Accordingly, an effective air conditioning system must include some control means to enable the maintenance of a temperature within a desired range notwithstanding variations in the air conditioning load which occur from time to time for the indicated and other reasons. Numerous mixing boxes* of the induction type have been suggested. For example, the rate at which primary conditioned air is delivered to the mixing box can be varied, with a compensating variation in the rate at which a flow of air, for example from a plenum, is induced into the mixing box for mixture with the primary air, so that a mixture flows from the box at a substantially constant rate, but the temperature varies depending upon the proportions of primary conditioned air and induced air in the mixture. A mixing box has also been suggested where the flow of primary air induces a flow of warm air from a plenum, a flow of neutral air from the space, or a mixture of plenum air and room air, depending upon the positions of thermostatically controlled dampers. It has further been suggested that primary conditioned air can be by-passed around the induction portion of a mixing box to provide a maximum flow of primary conditioned air, with no induction for times of peak load on an air conditioning system. FNT *See, for example, U.S. Pat. Nos. 3,390,720; 3,516,606; 3,583,477; 3,604,625; 3,610,522; 3,611,908; and 3,883,071.
U.S. Pat. No. 3,883,071 discloses and claims apparatus which can be a mixing box of the induction type or a combined fluidic valve and induction box for zone control of temperature in an air conditioning system. In either case, the apparaus receives primary conditioned air, and delivers that air as required, for air conditioning. A signal is established which varies as a function of the air conditioning load on the zone served by the apparatus, and the rate at which primary conditioned air is delivered to the zone is varied between a maximum and a predetermined lesser rate at which the minimum fresh air required for ventilation is supplied to the space as the air conditioning load on the space varies between a maximum and an intermediate load. The apparatus includes an induction nozzle for inducing a flow of air from outside, for mixing with primary conditioned air, so that such mixture is delivered to the zone.
When the air conditioning load on the zone is below the intermediate load, the induced flow from outside includes heated air, as required, for temperature control. Preferably, when the air conditioning load is below the intermediate load, the induced flow from outside is at a constant rate, and is heated air, e.g., from a plenum, or a mixture of heated air and neutral air from the zone.
The instant invention is based upon the discovery of improved apparatus for zone control of temperature in an air conditioning system. The apparatus, in some embodiments, is similar in function to the mixing box of U.S. Pat. No. 3,883,071, except that a fan rather than an induction nozzle is used to induce a flow of air; different means for controlling the flow of conditioned and recirculated air are also provided in some embodiments while, in still others, conventional and modified air bars are used in combination with other apparatus to accomplish the desired control. Apparatus is also provided wherein the rate at which primary conditioned air which includes air for ventilation, is delivered to the zone is varied between a maximum and a predetermined lesser rate as the air conditioning load on the space varies between a maximum and in intermediate load, and wherein, when the air conditioning load on the zone is below the intermediate load, primary conditioned air continues to be delivered at the predetermined lesser rate while an induced flow from outside includes heated air, as required, for temperature control, but wherein the necessity for establishing a signal which varies as a function of the air conditioning load is eliminated. The predetermined lesser rate at which primary air is delivered to the space under the stated conditions is one at which the minimum fresh air required for ventilation is supplied to the space by the primary conditioned air.